This invention relates to vertical gas metal-arc welding of metal plate. More particularly, the invention relates to two-sided vertical welding of thick plate, such as aluminum and its alloys, in a single welding pass on each surface of the plate.
It is known in the art that welding thick plate presents peculiar problems. For example, the thicker the plate, the more difficult it is to deposit high quality welds with efficiency. Methods known in the art for welding thick plate have achieved only varying success through the use of special joint geometry and other techniques. Conventionally, U, V, X or Y shaped edge preparations are used for one-sided and two-sided welding of thick plate. It is also known in the art that increasing the welding current increases weld efficiency and decreases the number of weld passes because of the resulting increase in the amount of molten metal deposited from the welding electrode wire. Furthermore, it is known that a reduction in the welding speed causes an increase in the deposited metal per unit length of the weld bead. Weld bead penetration can be increased by either increasing the welding current or decreasing the welding speed. Such adjustments, however, can present problems in the weld notch toughness and the sensitivity of the weld to its environment. Such considerations and problems are applicable generally to various metals and alloys, including steel alloy and aluminum alloy plates.
Although much effort has been made to improve various aspects of different thick plate welding processes, only limited success have been achieved. For example, U.S. Pat. No. 3,307,014, issued Feb. 28, 1967, relates to one pass butt welding from either one side or from both sides of the steel plate having I-shaped edges and the use of a flux cored wire. That method also contemplates using a backing member for supporting the flux. Electric arc welding of relatively thick steel plate from one side is shown in U.S. Pat. No. 3,351,734, issued Nov. 7, 1967, using an X-shaped groove and a backup plate. It is also known from U.S. Pat. No. 3,748,429, issued July 24, 1973, of a method of welding steel plate from both sides using at least two electrodes and a special joint geometry (Y or double V joints shown) which establishes the relationship between the depth of the groove and the root face width.
For all purposes herein, reference to "side" is used interchangeably with "surface" of the article or plate which is welded. For example, one-sided or two-sided welding refers to welding plate articles by depositing a weld bead on, respectively, one surface only or both surfaces.
Such prior art methods for welding plate on both sides have any one of several disadvantages. For example, extensive edge preparation of the plate before welding to form U, V, X or Y shaped grooves can add to the costs of welding. Furthermore, the cost of welding increases as the number of welding passes necessary to provide the required welding bead filler material increases. Also, more welding passes increase the labor cost of welding, i.e. time spent on the job, as well as increased shielding gas consumption. For methods of welding plate on both sides, back chipping is necessary for removing weld bead material from the back side of the plate to provide a clean weld surface prior to depositing the second weld. When back chipping is done manually, the overall welding costs rise with added labor costs.
It is desirable that an economical method be found for vertical gas metal-arc welding of thick plate, such as aluminum and its alloys. Such a method should provide a quality weld without incurring the costs attending specialized welding equipment, extensive edge preparation, and multiple welding passes.